1. Field of the Invention
The present invention relates to an unwrapping apparatus for unwrapping a load comprising a plurality of articles placed on a pallet and a film wrapping the articles, and in particular, the present invention relates to an improved unwrapping apparatus for unwrapping a stretch-wrapped or shrink-wrapped load including relatively light articles such as empty containers arranged in bulk on a pallet and stacked into a plurality of layers via separate sheets.
2. Description of the Related Art
Conventionally, a variety of empty containers, such as glass bottles, PET bottles, or metallic cans are delivered to a bottling plant, in the form of a palletized load in which containers are placed on a pallet in bulk and layered via separate sheets between the layers, and the load is shrink-wrapped or stretch-wrapped. Shrink-wrapping apparatuses and stretch-wrapping apparatuses that can automatically shrink-wrap or stretch-wrap empty containers are known.
Unwrapping apparatuses for automatically unwrapping a shrink-wrapped or stretch-wrapped palettized load are also known and disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) Nos. 48-58995, 49-95788, 1-111642, and 2-166033.
However, a problem has been pointed out regarding the unwrapping apparatuses. When the shrink-wrapped or stretch-wrapped palettized load including light articles such as empty containers is unwrapped, the wrapped articles such as containers fall off from the separate sheet.
In the case of unwrapping the stretch-wrapped load, the elastic stretchable film is wound around the articles under tension. When the film is cut, the film is suddenly released from tension and immediately shrinks while it is in contact with the surfaces of the articles, with the result that the articles such as light and empty containers stacked in bulk via separate sheet are pulled and moved by the film and possibly fall off from the separate sheets. The U.S. Pat. No. 5,282,346, assigned to the same assignee as for the present case, proposes an unwrapping apparatus which can solve this problem.
This unwrapping apparatus comprises front and rear upright frames, lower grippers arranged on the front upright frame for gripping a lower edge of a film on the load, a cutter unit arranged on the front upright frame for vertical movement along the front upright frame for cutting the film, and a carriage arranged on the rear upright frame for vertical movement along the rear upright frame. The carriage has a platen for stabilizing the load while being unwrapped, and a pair of symmetrical swing arms are arranged on the carriage. Upper grippers are carried by the free ends of the swing arms for gripping an upper edge of the film, so that the film that is cut by the cutter unit and gripped by the upper grippers is spread and separated from the load during a swing motion of the swing arms.
This unwrapping apparatus, however, is adapted for the stretch-wrapped load and cannot be applied to the shrink-wrapped load, since the film in the shrink-wrapped load is shaped in an inverted cup to cover the articles with the open bottom of the film located under the pallet and the bottom rims of the film are bent to the underside of the pallet and caught by the pallet at the bottom corners thereof. A heat is applied to the film to establish the shrink-wrapping. If this unwrapping apparatus is to be used for unwrapping the shrink-wrapped load, the top of the film of the load and the bottom corners of the film must be cut prior to the unwrapping operation by the unwrapping apparatus.
Japanese Patent Application No. 6-211817, assigned to the same assignee as for the present case, proposes a preliminary film cutting device which can be mounted to or arranged as a preparatory device for the above-described unwrapping apparatus. In this device, the upper portion of one side of the shrink-wrapped load, that is to be cut by the unwrapping apparatus, the upper portions of two sides adjacent to said one side, and the bottom corners of the film are cut prior to the operation by the unwrapping apparatus.
However, this preliminary film cutting device also suffers from several problems. When the upper portion of the sides of the film of the shrink-wrapped load is cut, the top edge of the load is damaged. If the articles and the pallet are fastened by vertically surrounding bands, the bands may be severed, and the articles are loosened and cannot be stably conveyed to the unwrapping apparatus. Furthermore, even ven if the bottom corners of the film are cut, the lower portion of the film may sometimes be caught by the pallet and thus not completely separated from the pallet.